PROJECT SUMMARY Of the 29 million persons living with HIV (PLHIV) in sub-Saharan Africa, only half are aware of their seropositivity, and among these, less than half are on HIV antiretroviral therapy (ART). The average CD4+ T-lymphocyte cell count at ART initiation in sub-Saharan Africa was 140 cells/mm3 as of 2012, demonstrating that late-stage disease at presentation to care and at ART initiation remain the norm. The stigma attached to HIV has been identified as a critical barrier to improving these HIV prevention and treatment outcomes. HIV remains heavily stigmatized throughout sub-Saharan Africa and has only been partially mitigated by current interventions. The scientific objective of this R01 application is to apply social network methods to understand the social production of HIV stigma, its propagation over time through the social network, and its causal effects on HIV prevention and treatment outcomes. Our central hypothesis is that injunctive norms (i.e., the prevailing attitude within the social network about what constitutes approved or disapproved conduct) have a causal effect on one's own beliefs, and that the effect is mediated by anticipated stigma (i.e., what one perceives to be the prevailing attitude). We further hypothesize that injunctive norms, anticipated stigma, and one's own beliefs exert independent causal effects on HIV prevention among those at risk for HIV infection and on HIV treatment outcomes among PLHIV. These hypotheses have been formulated on the basis of our strong preliminary data from rural Uganda showing that injunctive norms are associated with one's own negative attitudes toward PLHIV, and that HIV stigma is associated with a wide range of adverse HIV prevention and treatment outcomes. We recently completed a population-based, sociocentric social network study of N=1,814 adults in rural Uganda. This R01 application will extend our pilot study into a cohort, following these same participants and any new in-migrants over time, so that we can accomplish the following specific aims: (1) Estimate the causal effect of injunctive norms on negative attitudes toward PLHIV; (2) Estimate the causal effects of injunctive norms, anticipated stigma, and negative attitudes toward PLHIV on uptake of voluntary counseling and testing, condomless sexual intercourse, and HIV infection among HIV-negative persons and persons of unknown serostatus; and (3) Estimate the causal effects of injunctive norms, anticipated stigma, and internalized stigma on depression, linkage to care, ART adherence, viral suppression, retention in care, & secondary transmission risk among PLHIV. Our key innovation is that we use photograph-based identity verification to collect longitudinal, sociocentric social network data, and we apply analytic methods designed to identify causal effects and causal mediation effects. The proposed study will have significant public health impact by laying a foundation for developing more effective anti-stigma interventions and by identifying where in the dynamic process of stigma formation these interventions can most strategically be deployed.